WO2011018816A1 - Optical or radiation imaging device - Google Patents

Optical or radiation imaging device Download PDF

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Publication number
WO2011018816A1
WO2011018816A1 PCT/JP2009/003837 JP2009003837W WO2011018816A1 WO 2011018816 A1 WO2011018816 A1 WO 2011018816A1 JP 2009003837 W JP2009003837 W JP 2009003837W WO 2011018816 A1 WO2011018816 A1 WO 2011018816A1
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WIPO (PCT)
Prior art keywords
conversion layer
temperature
light
radiation imaging
ray
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PCT/JP2009/003837
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French (fr)
Japanese (ja)
Inventor
田邊晃一
徳田敏
貝野正知
岸原弘之
吉牟田利典
Original Assignee
株式会社島津製作所
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Priority to PCT/JP2009/003837 priority Critical patent/WO2011018816A1/en
Publication of WO2011018816A1 publication Critical patent/WO2011018816A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14665—Imagers using a photoconductor layer
    • H01L27/14676—X-ray, gamma-ray or corpuscular radiation imagers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
    • H04N25/63—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to dark current
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/30—Transforming light or analogous information into electric information
    • H04N5/32—Transforming X-rays

Definitions

  • the present invention relates to a light or radiation imaging apparatus used in the medical field, industrial fields such as non-destructive inspection, RI (Radio Isotope) inspection, and optical inspection, and in particular, a conversion layer that converts light or radiation into a charge signal.
  • the present invention relates to a light or radiation imaging apparatus provided with a means for measuring the temperature.
  • a light or radiation imaging apparatus is provided with a light or radiation detector for detecting light or radiation.
  • light refers to infrared rays, visible rays, ultraviolet rays, radiation, ⁇ rays, and the like, and in particular, X-rays will be described as an example.
  • X-ray detectors that detect X-rays using an active matrix substrate are widely used as X-ray detectors. This is because if an active matrix substrate is used, the X-ray detection value of each pixel can be read, which is very useful.
  • an X-ray conversion layer made of a semiconductor is stacked on an active matrix substrate, an X-ray detection element for each active element can be formed.
  • Patent Document 1 discloses that the temperature of the X-ray flat panel detector is measured using a temperature sensor. When the temperature data measured by the temperature sensor deviates from a predetermined temperature range, the monitor is warned that the temperature has deviated and power supply to the X-ray flat panel detector is stopped. In this way, crystallization of a-Se is prevented.
  • JP 2006-128890 A JP 2006-128890 A
  • the temperature sensor is mounted on the surface of the X-ray conversion layer of the X-ray flat panel detector, the X-ray conversion layer becomes a shadow of the temperature sensor. Projected and the X-ray transmission image of the subject cannot be detected accurately. In order to prevent this, the temperature sensor is attached to a housing that covers the X-ray flat panel detector or attached to a pixel that does not detect X-rays. For this reason, the exact temperature of the X-ray conversion layer could not be measured during X-ray imaging.
  • the present invention has been made in view of such circumstances, and an object thereof is to provide a light or radiation imaging apparatus capable of accurately measuring the temperature state of a conversion layer sensitive to light or radiation. .
  • the present invention has the following configuration. That is, the light or radiation imaging apparatus according to the present invention includes a conversion layer that converts light or radiation into a charge signal in the light or radiation imaging apparatus, and the charge signal for each detection element obtained by dividing the conversion layer into a two-dimensional matrix. Reading means, a charge voltage conversion means for converting a charge signal read from the reading means into a voltage signal, and a dark current component flowing through the conversion layer included in the voltage signal, the temperature of the conversion layer is determined. And a conversion layer temperature calculation unit to be obtained.
  • the charge signal converted from light or radiation in the conversion layer is read for each detection element divided into a two-dimensional matrix and converted into a voltage signal by the charge-voltage conversion means. Converted. Among the components constituting this voltage signal, the temperature of the conversion layer can be measured based on the dark current component flowing in the conversion layer.
  • the conversion layer temperature calculation unit can obtain the temperature of the conversion layer from the relational expression between the dark current component flowing through the conversion layer in the voltage signal and the temperature. Thereby, the exact temperature of the conversion layer can be measured. Moreover, the conversion layer temperature calculation part can also obtain
  • the conversion layer is divided into a main pixel region and a correction pixel region, and includes a temperature distribution calculation unit that calculates a two-dimensional temperature distribution in the conversion layer in the main pixel region, so that the temperature of the conversion layer in the correction pixel region
  • the temperature distribution of the conversion layer in the main pixel region can be measured.
  • the main pixel region is further divided into a plurality of detection pixel regions, the two-dimensional temperature distribution for each detection pixel region can also be measured.
  • the temperature distribution can be measured at a higher speed than the measurement of the two-dimensional temperature distribution for each detection element.
  • a dark current component calculation unit that obtains a dark current component in a voltage signal for each detection element from a two-dimensional temperature distribution of the conversion layer
  • an amplifier noise removal unit that removes amplifier noise that does not vary with temperature
  • the correction pixel region may be disposed at one end of the conversion layer, may be disposed at both ends of the conversion layer, or is disposed at the end along the four sides of the conversion layer. It may be a thing.
  • the material of the conversion layer may be CdTe or CdZnTe (cadmium zinc telluride) or a-Se. If the material of the conversion layer is CdTe or CdZnTe, it is possible to provide a light or radiation imaging apparatus capable of removing noise due to dark current that fluctuates in temperature. Further, if the material of the conversion layer is a-Se, the temperature of the conversion layer can be accurately measured, so that a light or radiation imaging apparatus that can prevent crystallization can be provided.
  • the light or radiation imaging apparatus can provide a light or radiation imaging apparatus that can accurately measure the temperature state of the conversion layer sensitive to light or radiation.
  • FIG. 1 is a block diagram illustrating an overall configuration of an X-ray imaging apparatus according to an embodiment
  • FIG. 2 is a block diagram illustrating a configuration of an X-ray flat panel detector included in the X-ray imaging apparatus
  • FIG. 3 is an X-ray plane
  • FIG. 4 is a schematic longitudinal sectional view around the X-ray conversion layer of the detector
  • FIG. 4 is a circuit diagram showing the configuration of the charge-voltage converter.
  • X-rays will be described as an example of incident light or radiation
  • an X-ray imaging apparatus will be described as an example of a radiation imaging apparatus.
  • the X-ray imaging apparatus performs imaging by irradiating a subject with X-rays. Specifically, an X-ray image transmitted through the subject is projected on the X-ray conversion layer, and a charge signal (carrier) proportional to the density of the image is generated in the X-ray conversion layer.
  • the X-ray imaging apparatus transmits an X-ray tube 1 that irradiates a subject M to be imaged with X-rays, a top plate 2 on which the subject M is placed, and the subject M.
  • An X-ray flat panel detector (hereinafter referred to as FPD) 3 for converting into a charge signal corresponding to the X-ray dose (detecting the X-ray as a charge signal), and further converting the charge signal into a voltage signal and outputting the voltage signal;
  • a / D converter 4 for converting the voltage signal output from the analog to digital, and an image processing unit 5 for processing the digital voltage signal converted by the A / D converter 4 to construct an X-ray fluoroscopic image
  • a main control unit 6 that performs various controls related to X-ray imaging, an X-ray tube control unit 7 that controls the X-ray tube 1 by generating a tube voltage and a tube current based on the control of the main control unit 6;
  • Processed by the input unit 8 capable of performing
  • the FPD 3 includes an X-ray detection unit XD1 having a plurality of X-ray detection elements DU, a gate drive circuit 11, a charge voltage conversion unit 12, a sample and hold unit 13, and a multiplexer 14. .
  • the plurality of X-ray detection elements DU are connected to the gate drive circuit 11 by gate lines GL1 to GL10, and are connected to the charge / voltage converter 12 by data lines DL1 to DL10.
  • the X-ray detection element DU corresponds to the detection element in the present invention
  • the charge voltage conversion unit 12 corresponds to the charge voltage conversion means in the present invention.
  • the X-ray detection elements DU output charge signals in response to incident X-rays, and are arranged in a vertical and horizontal two-dimensional matrix form on the X-ray detection unit XD1 where X-rays are incident.
  • the X-ray detection elements DU arranged in a two-dimensional matrix of 10 ⁇ 10 are shown as an example.
  • the actual X-ray detection unit XD1 includes the X-ray detection elements DU.
  • the X-ray detection part XD1 in the FPD 3 is divided into a main pixel area A1 and a correction pixel area B1.
  • the correction pixel region B1 is disposed at the left end of the X-ray detection unit XD1.
  • the X-ray detection element DU arranged in the main pixel area A1 is for measuring the amount of radiation transmitted through the subject M
  • the X-ray detection element DU arranged in the correction pixel area B1 is X This is for measuring the temperature of the X-ray conversion layer in the line detector XD1.
  • a lead seal or the like for preventing X-ray incidence is attached on the X-ray detection element DU in the correction pixel region B1.
  • the X-ray detection element DU includes a voltage application electrode 16 that applies a high bias voltage Va, an X-ray conversion layer 17 that converts an incident X-ray into a charge signal, and an X-ray conversion layer. And an active matrix substrate 18 for accumulating and reading out (outputting) the charge signal converted at 17.
  • the X-ray conversion layer 17 is divided by the X-ray detection elements DU into a two-dimensional matrix to detect X-rays.
  • the active matrix substrate 18 corresponds to the reading means in the present invention.
  • the X-ray conversion layer 17 is made of an X-ray sensitive semiconductor and is made of, for example, amorphous a-Se or a polycrystalline compound CdTe or CdZnTe. Further, when X-rays are incident on the X-ray conversion layer 17, a predetermined number of carriers (charge signals) proportional to the energy of the X-rays are directly generated (direct conversion type). Further, the generated charge signal is collected for each pixel electrode 20 based on the application of the bias voltage Va to the voltage application electrode 16.
  • the active matrix substrate 18 is provided with an insulating glass substrate 19, on which a capacitor Ca that accumulates a charge signal collected for each pixel electrode 20 and a switching element.
  • a thin film transistor (hereinafter referred to as TFT) 21, gate lines GL 1 to GL 10 for controlling the TFT 21 from the gate driving circuit 11, and data lines DL 1 to DL 10 for reading out charge signals from the TFT 21 are provided.
  • the gate drive circuit 11 operates the TFT 21 of each X-ray detection element DU in order to selectively extract the charge signals detected by the X-ray detection elements DU.
  • the gate drive circuit 11 sequentially selects the gate lines GL1 to GL10 connected in common for each row of the X-ray detection elements DU and sends a gate signal.
  • the TFTs 21 of the X-ray detection elements DU in the selected row are simultaneously switched on by the gate signal, and the charge signal stored in the capacitor Ca is output to the charge / voltage conversion unit 12 through the data lines DL1 to DL10. .
  • the charge-voltage conversion unit 12 includes a number of charge-voltage conversion amplifiers 22 as shown in FIG. 4 corresponding to the data lines DL1 to DL10 for each column of the X-ray detection elements DU (10 in FIG. 2). It has been.
  • the charge-voltage conversion amplifier 22 is a charge detection amplification circuit (CSA: Charge Sensitive Amplifier) that converts a charge signal output from each X-ray detection element DU into a voltage signal.
  • CSA Charge Sensitive Amplifier
  • the charge voltage conversion amplifier 22 converts the charge signals read from the data lines DL1 to DL10 into voltage signals and outputs them to the sample and hold unit 13.
  • the charge voltage conversion unit 12 corresponds to the charge voltage conversion means in the present invention.
  • the sample and hold unit 13 is provided with a number of sample and hold circuits corresponding to the number of charge-voltage conversion amplifiers 22.
  • the sample and hold circuit samples the voltage signal output from the charge-voltage conversion amplifier 22 at a predetermined time.
  • the voltage signal at the time when a predetermined time has elapsed is held (held), and the voltage signal in a stable state is output to the multiplexer 14.
  • the number of switches corresponding to the number of sample and hold circuits is provided inside the multiplexer 14. Any one of the switches is sequentially switched to the ON state, and is output to the A / D converter 4 as a time division signal obtained by bundling one voltage signal output from each sample hold circuit.
  • the A / D converter 4 samples the voltage signal from the multiplexer 14 at a predetermined timing, converts it to a digital voltage signal, and outputs it to the image processing unit 5.
  • the image processing unit 5 includes an image memory unit 23, an amplifier noise removing unit 24, a temperature fluctuation noise processing unit 25, and an image configuration unit 26.
  • a conversion layer temperature calculation unit 27, a conversion layer temperature distribution calculation unit 28, a temperature variation noise calculation unit 29, and a temperature variation noise removal unit 30 are further provided.
  • the image processing unit 5 removes amplifier noise and temperature fluctuation noise from the voltage signal transferred from the FPD 3 via the A / D converter 4 to form an X-ray fluoroscopic image.
  • a voltage signal transferred to the image processing unit 5 (hereinafter referred to as a detection voltage signal) can be divided into three components depending on the cause of the voltage signal. That is, the detection voltage signal is composed of the X-ray transmission image signal, the temperature variation noise Nt, and the temperature non-variation noise 32.
  • Detection voltage signal (X-ray transmission image signal) + (Temperature fluctuation noise) + (Temperature non-fluctuation noise)
  • the X-ray transmission image signal is a voltage signal based on a charge signal obtained by converting the X-ray transmitted through the subject M by the X-ray conversion layer 17 and is a voltage signal necessary for reconstructing the X-ray fluoroscopic image. .
  • the temperature fluctuation noise Nt is a noise signal obtained by converting the dark current flowing in the X-ray conversion layer 17 as a voltage signal, and its value varies sensitively depending on the temperature of the X-ray conversion layer 17.
  • the temperature fluctuation noise Nt can be generally expressed by the following equation.
  • Nt ⁇ (exp ( ⁇ / T) ⁇ 1), ( ⁇ , ⁇ : constant, T: absolute temperature [K]) (1)
  • the temperature non-varying noise 32 is a noise signal that is always substantially constant and is not affected by the temperature condition in which the FPD 3 is used.
  • the temperature non-variation noise 32 is a noise signal generated due to an amplifier offset in the charge-voltage conversion unit 12.
  • Both the temperature fluctuation noise Nt and the temperature non-variation noise 32 reduce the dynamic range of the X-ray transmission image signal. Further, the temperature of the environment in which the X-ray imaging apparatus is installed is constantly changing even if air conditioning is performed. When the temperature fluctuation noise Nt appears on the X-ray fluoroscopic image due to temperature change, an accurate X-ray fluoroscopic image is displayed. Can't get.
  • FIG. 5 illustrates the temperature fluctuation noise Nt and the temperature non-variation noise 32.
  • the temperature fluctuation noise Nt varies exponentially with respect to the temperature T due to the nature of dark current.
  • the dark image voltage signal obtained when the X-ray tube 1 does not irradiate X-rays can be divided into two components.
  • (Dark image voltage signal) (Temperature fluctuation noise) + (Temperature non-variation noise)
  • the detection voltage signal can be composed of two components depending on conditions.
  • (Detection voltage signal) (X-ray transmission image signal) + (dark image voltage signal) (however, temperature is constant)
  • the above formula is established only when the temperature of the X-ray conversion layer 17 is the same between the X-ray transmission imaging and the dark image imaging.
  • the dark image voltage signal D can be expressed by the following equation.
  • ⁇ and ⁇ in the formulas (1) and (2) are values that vary depending on the constituent material and the constituent state of the X-ray conversion layer 17, and ⁇ is substantially constant regardless of the temperature.
  • Three constants ⁇ , ⁇ , and ⁇ can be obtained by measuring the dark image voltage signal during dark images while changing the temperature.
  • the values of the three constants ⁇ , ⁇ , and ⁇ in the equation (2) are obtained by measuring the values of the dark image voltage signals at the points of the temperatures T1, T2, and T3 of the X-ray conversion layer 17. Ask.
  • an approximate expression of the temperature fluctuation noise Nt can be obtained from the value of the dark image voltage signal.
  • the measurement of the temperature and the dark image voltage signal is not limited to three points, and as the number of measurement points is increased, a more accurate approximate expression can be obtained.
  • the dark image voltage signal may be measured when the environmental temperature where the FPD 3 is installed is accurately set to T1, T2, and T3, and the temperature of the X-ray conversion layer 17 may be accurately measured.
  • the dark image voltage signal at three different temperatures T1, T2, and T3 may be measured.
  • a look-up table of temperature and temperature fluctuation noise Nt may be created from values of dark image voltage signals obtained by measuring characteristic curves of temperature fluctuation noise Nt at three or more temperatures. In this way, an approximate expression or a look-up table between the temperature and the temperature fluctuation noise for each X-ray detection element DU can be created. This approximate expression corresponds to the relational expression in the present invention, and the lookup table corresponds to the correspondence table in the present invention.
  • the digital voltage signal output from the A / D converter 4 is temporarily stored in the image memory unit 23. Further, as will be described later, a voltage signal obtained by removing the temperature non-varying noise component ⁇ from the detected voltage signal is also temporarily stored.
  • the amplifier noise removal unit 24 stores a ⁇ value that is a temperature non-variable noise component in advance, and removes the temperature non-variable noise component ⁇ from the detected voltage signal.
  • the value of the detection voltage signal from which the temperature non-variation noise component ⁇ has been removed is stored again in the image memory unit 23.
  • the detected voltage signal is a dark image voltage signal
  • the value of the dark image voltage signal from which the temperature non-varying noise component ⁇ is removed is sent to the conversion layer temperature calculation unit 27 in order to measure the temperature of the X-ray conversion layer 17. Sent.
  • the conversion layer temperature calculation unit 27 includes a temperature conversion approximate expression or a lookup table, and calculates the temperature of the X-ray conversion layer 17 from the voltage signal obtained by removing the temperature non-varying noise component ⁇ from the dark image voltage signal. calculate.
  • the calculated temperature is also transferred to the main control unit 6, and when the temperature is higher than the specified temperature, a warning can be issued on the display unit 9. Further, as an emergency measure, the power supply to the FPD 3 may be cut or the FPD 3 may be cooled by a separate cooling device according to a command from the main control unit 6.
  • the conversion layer temperature distribution calculation unit 28 includes temperature distribution characteristics of all X-ray detection pixels DU provided in the X-ray detection unit XD1 as a function or a lookup table. If the temperature of the X-ray conversion layer 17 of a specific X-ray detection element DU is known, the temperature distribution characteristics of the X-ray conversion layers 17 in all the X-ray detection elements DU provided in the X-ray detection unit XD1 are calculated. be able to.
  • the temperature fluctuation noise calculation unit 29 calculates the temperature fluctuation noise Nt generated in each X-ray detection element DU from the calculated temperature of the X-ray conversion layer 17 in each X-ray detection element DU.
  • the temperature fluctuation noise calculation unit 29 is provided with an approximate expression or look-up table of the temperature fluctuation noise Nt of each X-ray detection element DU created in advance, and calculates the temperature fluctuation noise Nt from this.
  • the temperature fluctuation noise removing unit 30 removes the corresponding temperature fluctuation noise Nt from the voltage signal from which the temperature non-variation noise 31 has been removed from the detection voltage signal of each X-ray detection element DU, whereby the X-ray detection element DU. X-ray transmission image signals for each can be obtained.
  • the image construction unit 26 constructs an X-ray fluoroscopic image from the X-ray transmission image signal. In addition to the X-ray fluoroscopic image, a tomographic image can be reconstructed at the time of CT imaging.
  • the configured fluoroscopic image is transferred to the main control unit 6 and displayed on the display unit 9 or stored in the storage unit 10.
  • the main control unit 6 controls the X-ray tube control unit 7 and the FPD 3.
  • the X-ray tube control unit 7 controls the X-ray tube 1 by generating tube voltage and tube current based on the control from the main control unit 6, and the subject M is irradiated with X-rays from the X-ray tube 1. Further, the X-ray transmitted through the subject M is converted into a charge signal corresponding to the X-ray dose transmitted through the subject M by the X-ray detection element DU of the FPD 3. The converted charge signal is accumulated by the capacitor Ca.
  • the gate drive circuit 11 sequentially selects the gate lines.
  • description will be made assuming that gate lines G1, G2, G3,..., G9, G10 are selected one by one in order.
  • the gate drive circuit 11 selects the gate line G1, and each X-ray detection element DU connected to the gate line G1 is designated.
  • a voltage is applied to the gate of the TFT 21 of each designated X-ray detection element DU when a gate signal is sent to the ON state.
  • the charge signal stored in the capacitor Ca connected to each designated TFT 21 is read out to the data lines DL1 to DL10 via the TFT 21.
  • the gate drive circuit 11 selects the gate line G2, and in the same procedure, each X-ray detection element DU connected to the gate line G2 is designated, and the capacitor of each designated X-ray detection element DU is designated.
  • the charge signal stored in Ca is read out to the data lines DL1 to DL10.
  • the remaining gate lines G3 to G10 are sequentially selected to read out charge signals in a two-dimensional manner.
  • the gate drive circuit 11 sequentially selects the gate lines GL1 to GL10, so that the X-ray detection element DU connected to each gate line is designated, and the capacitor Ca of each designated X-ray detection element DU.
  • the charge signal stored in is read to the data lines DL1 to DL10.
  • the charge signal read out to each data line is converted into a voltage signal and amplified by the charge-voltage conversion amplifier 22 in the charge-voltage conversion unit 12.
  • the sample and hold unit 13 samples and holds the voltage signal converted by the charge / voltage conversion unit 12 once. Thereafter, the voltage signal held in the sample and hold unit 13 from the multiplexer 14 is sequentially output as a time division signal.
  • the output voltage signal is converted from an analog value to a digital value by the A / D converter 4.
  • the image processing unit 5 Based on the converted digital signal, the image processing unit 5 performs signal processing to form a two-dimensional captured image.
  • a voltage signal sent from the X-ray detection element DU in the main pixel region A1 to the image processing unit 5 is used as a main pixel voltage signal, and a voltage signal sent from the X-ray detection element DU in the correction pixel region B1 to the image processing unit 5 Is a correction voltage signal. Since the correction pixel region B1 is shielded with lead tape against X-rays, the correction voltage signal is a dark image voltage signal.
  • the main pixel voltage signal and the correction pixel signal are composed of the following signal components.
  • the main pixel voltage signal and the correction voltage signal sent to the image processing unit 5 are stored in the image memory unit 23 and transferred to the amplifier noise removing unit 24.
  • the amplifier noise removing unit 24 removes the temperature non-varying noise component ⁇ stored in advance from the transferred main pixel voltage signal and correction voltage signal. Thereafter, the main pixel voltage signal from which the temperature non-varying noise component ⁇ has been removed is stored again in the image memory unit 23, and the correction voltage signal from which the temperature non-varying noise component ⁇ has been removed is transferred to the conversion layer temperature calculating unit 27. .
  • the conversion layer temperature calculation unit 27 calculates the temperature of the X-ray conversion layer 17 for each X-ray detection element DU arranged in the correction pixel region B1 from the correction voltage signal from which the temperature non-varying noise component ⁇ is removed. The The temperature data is transferred to the conversion layer temperature distribution calculation unit 28.
  • the conversion layer temperature distribution calculation unit 28 calculates the two-dimensional temperature distribution of the main pixel area A1 from the transferred temperature data of the correction pixel area B1.
  • the calculated two-dimensional temperature distribution data is transferred to the temperature fluctuation noise calculation unit 29.
  • the temperature fluctuation noise calculation unit 29 calculates temperature fluctuation noise for each X-ray detection element DU in the main pixel area A1 from the transferred two-dimensional temperature distribution data.
  • the temperature fluctuation noise of each X-ray detection element DU is transferred to the temperature fluctuation noise removing unit 30.
  • the temperature fluctuation noise removal unit 30 removes the temperature fluctuation noise transferred from the corresponding temperature fluctuation noise calculation unit 29 from the main pixel voltage signal from which the temperature non-fluctuation noise component ⁇ stored in the image memory unit 23 is removed. Thus, an X-ray transmission image signal for each X-ray detection element DU can be obtained. The X-ray transmission image signal is transferred to the image construction unit 26.
  • the image construction unit 26 constructs an X-ray fluoroscopic image of the subject M from the transferred X-ray transmission image signal.
  • the configured X-ray fluoroscopic image is displayed on the display unit 9 via the main control unit 6.
  • the X-ray fluoroscopic image obtained as described above has both temperature fluctuation noise and temperature non-variation noise removed, a clear image can be obtained. Further, it is possible to obtain an X-ray fluoroscopic image that is not changed by the temperature of the imaging environment. In addition, even when capturing a moving image, temperature fluctuation noise can be removed in real time. Further, the temperature of the conversion layer 17 can be measured as a two-dimensional temperature distribution.
  • the present invention is not limited to the above embodiment, and can be modified as follows.
  • the temperature fluctuation noise of each X-ray detection pixel DU is calculated.
  • the temperature fluctuation for each region constituted by a plurality of X-ray detection pixels DU. Noise may be calculated. That is, the temperature fluctuation noise of each X-ray detection pixel DU in the same detection pixel region is set to the same value.
  • the main pixel area of the X-ray detector XD2 of the FPD 33 is divided into nine detection pixel areas A2 to A10.
  • the number of detection pixel regions into which the main pixel region is divided may be arbitrarily determined depending on whether the accuracy of the two-dimensional temperature distribution is obtained or the measurement time of the two-dimensional temperature distribution is reduced.
  • a relational expression or a look-up table between the average value of the dark current flowing through the X-ray conversion layer 17 and the temperature may be created for each detection pixel region. Further, since the temperature fluctuation noise is calculated for each detection pixel region, the processing time can be shortened, rather than calculating the temperature fluctuation noise from the temperature measured for each X-ray detection element DU.
  • the correction pixel area B1 is arranged at the left end of the X-ray detection units XD1 and XD2, but it may be arranged at any one of the upper, lower, left and right ends. Further, not only one end but also correction pixel regions B1 and B2 may be provided at both left and right ends of the X-ray detection unit XD3 of the FPD 34 as shown in FIG. In this case, the upper and lower ends are not limited to the left and right ends.
  • correction pixel regions B3 to B6 may be arranged at all the upper, lower, left and right ends of the X-ray detection unit XD4 of the FPD 35. That is, correction pixel regions B3 to B6 are arranged at the end portions along the four sides of the X-ray detection unit XD4. Thereby, the calculation accuracy of the two-dimensional temperature distribution in the main pixel region A13 can be improved.
  • the temperature of the X-ray conversion layer 17 is measured by the conversion layer temperature calculation unit 27 based on the correction voltage signal from the correction pixel region B1.
  • the temperature of the X-ray conversion layer 17 in each X-ray detection element DU may be measured by the conversion layer temperature calculation unit 27 based on the dark image voltage signal of the X-ray detection element DU.
  • the temperature of the X-ray conversion layer 17 is measured based on the correction voltage signal from the correction pixel region B1, but a temperature sensor is directly attached to the correction pixel region B1, Based on the temperature data from the temperature sensor, the temperature fluctuation noise in the main pixel region A1 may be removed.
  • the X-ray detection element DU is an X-ray sensitive semiconductor that is sensitive to X-rays. However, if a light-sensitive semiconductor is employed, the temperature of the conversion layer is measured with the same configuration. An optical imaging device that can be used can be manufactured.

Abstract

A radiation imaging device wherein a conversion layer in which light or radiation is converted into a charge signal is provided in an X-ray plane detector (3).  The charge signal converted in the conversion layer is read for each of all detected elements divided in the form of a two-dimensional matrix and is converted into a voltage signal by a charge/voltage converting means. The temperature of the conversion layer can be measured by a conversion layer temperature calculating section (27) on the basis of a dark-current component flowing through the conversion layer in components constituting the voltage signal.  The temperature of the conversion layer is measured on the basis of the dark-current component, so that the temperature thereof can be directly measured.

Description

光または放射線撮像装置Light or radiation imaging device
　本発明は、医療分野や非破壊検査、ＲＩ（Radio Isotope）検査、および光学検査などの産業分野などで用いられる光または放射線撮像装置に係り、特に、光または放射線を電荷信号へ変換する変換層の温度を測定する手段を備えた光または放射線撮像装置に関するものである。 The present invention relates to a light or radiation imaging apparatus used in the medical field, industrial fields such as non-destructive inspection, RI (Radio Isotope) inspection, and optical inspection, and in particular, a conversion layer that converts light or radiation into a charge signal. The present invention relates to a light or radiation imaging apparatus provided with a means for measuring the temperature.
　従来、光または放射線撮像装置には、光または放射線を検出する光または放射線検出器を備えている。ここで光とは、赤外線、可視光線、紫外線、放射線、γ線等をいうが、特にＸ線を例に採って説明する。Ｘ線検出器には、アクティブマトリックス基板を用いてＸ線を検出するＸ線平面検出器が広く使われている。アクティブマトリックス基板を使うと、各画素のＸ線検出値を読み込むことができ、非常に有用だからである。さらに、アクティブマトリックス基板上に半導体からなるＸ線変換層を積層すると、アクティブ素子ごとのＸ線検出素子を形成することができる。 Conventionally, a light or radiation imaging apparatus is provided with a light or radiation detector for detecting light or radiation. Here, light refers to infrared rays, visible rays, ultraviolet rays, radiation, γ rays, and the like, and in particular, X-rays will be described as an example. X-ray detectors that detect X-rays using an active matrix substrate are widely used as X-ray detectors. This is because if an active matrix substrate is used, the X-ray detection value of each pixel can be read, which is very useful. Furthermore, when an X-ray conversion layer made of a semiconductor is stacked on an active matrix substrate, an X-ray detection element for each active element can be formed.
　Ｘ線を電荷信号に変換するＸ線変換層にａ－Ｓｅ（アモルファスセレン）を用いる場合、非晶質であるａ－Ｓｅが４０℃より高温になると結晶化が進行するので、Ｘ線変換層としての機能が永久に失われてしまう問題がある。また、近年、Ｘ線変換層として研究されている多結晶化合物半導体であるＣｄＴｅ（テルル化カドミウム）を主原料とするＸ線変換層においては、そのＸ線変換層の温度変化により暗電流の値がａ－Ｓｅに比べて大きく変化する問題がある。 When a-Se (amorphous selenium) is used for an X-ray conversion layer that converts X-rays into a charge signal, crystallization proceeds when amorphous a-Se is higher than 40 ° C. There is a problem that the function is lost forever. In addition, in an X-ray conversion layer using CdTe (cadmium telluride), which is a polycrystalline compound semiconductor, which has been studied as an X-ray conversion layer in recent years, a dark current value due to a temperature change of the X-ray conversion layer. However, there is a problem that changes greatly compared to a-Se.
　このように、ａ－Ｓｅにおいても、多結晶化合物半導体においても、そのＸ線変換層の温度を制御することは重要であり、そのためにはＸ線変換層の温度状況を測定する必要がある。 Thus, in both a-Se and polycrystalline compound semiconductors, it is important to control the temperature of the X-ray conversion layer. For this purpose, it is necessary to measure the temperature state of the X-ray conversion layer.
　Ｘ線変換層の温度状況を測定するために、特許文献１には、Ｘ線平面検出器の温度を温度センサを用いて測定することが開示されている。この温度センサによって測定された温度データが所定の温度範囲を逸脱した場合、モニタに温度が逸脱していることを警告するとともにＸ線平面検出器への給電を停止する。このようにしてａ－Ｓｅの結晶化を防いでいる。
特開２００６－１２８８９０号公報 In order to measure the temperature state of the X-ray conversion layer, Patent Document 1 discloses that the temperature of the X-ray flat panel detector is measured using a temperature sensor. When the temperature data measured by the temperature sensor deviates from a predetermined temperature range, the monitor is warned that the temperature has deviated and power supply to the X-ray flat panel detector is stopped. In this way, crystallization of a-Se is prevented.
JP 2006-128890 A
　しかしながら、Ｘ線平面検出器のＸ線変換層の面上に温度センサを取り付けると、Ｘ線変換層は温度センサの陰となるので、Ｘ線が入射すると温度センサの影がＸ線変換層に投影され、被検体のＸ線透過像を正確に検出できなくなる。これを防ぐために、温度センサはＸ線平面検出器を覆う匡体に取り付けるか、Ｘ線検出をしない画素上に取り付けていた。このため、Ｘ線撮像中にＸ線変換層の正確な温度を測定することはできなかった。 However, when a temperature sensor is mounted on the surface of the X-ray conversion layer of the X-ray flat panel detector, the X-ray conversion layer becomes a shadow of the temperature sensor. Projected and the X-ray transmission image of the subject cannot be detected accurately. In order to prevent this, the temperature sensor is attached to a housing that covers the X-ray flat panel detector or attached to a pixel that does not detect X-rays. For this reason, the exact temperature of the X-ray conversion layer could not be measured during X-ray imaging.
　また、Ｘ線変換層の検出面の２次元温度分布を正確に測定するためには、温度センサを多数個かつＸ線変換層の中央部にも取り付けなければならず、Ｘ線平面検出器が大画面化するほど取り付けが困難になる。 In addition, in order to accurately measure the two-dimensional temperature distribution on the detection surface of the X-ray conversion layer, a number of temperature sensors must be attached to the center of the X-ray conversion layer, and the X-ray flat panel detector The larger the screen, the more difficult it is to install.
　本発明は、このような事情に鑑みてなされたものであって、光または放射線に感応する変換層の温度状況を精度よく測定することができる光または放射線撮像装置を提供することを目的とする。 The present invention has been made in view of such circumstances, and an object thereof is to provide a light or radiation imaging apparatus capable of accurately measuring the temperature state of a conversion layer sensitive to light or radiation. .
　この発明は、このような目的を達成するために、次のような構成をとる。
　すなわち、この発明の光または放射線撮像装置は、光または放射線撮像装置において、　光または放射線を電荷信号へ変換する変換層と、前記変換層を２次元マトリックス状に分割した検出素子ごとに前記電荷信号を読み出す読み出し手段と、前記読み出し手段から読み出される電荷信号を電圧信号に変換する電荷電圧変換手段と、前記電圧信号に含まれる前記変換層を流れる暗電流成分を基に、前記変換層の温度を求める変換層温度算出部とを備えたことを特徴とする。 In order to achieve such an object, the present invention has the following configuration.
That is, the light or radiation imaging apparatus according to the present invention includes a conversion layer that converts light or radiation into a charge signal in the light or radiation imaging apparatus, and the charge signal for each detection element obtained by dividing the conversion layer into a two-dimensional matrix. Reading means, a charge voltage conversion means for converting a charge signal read from the reading means into a voltage signal, and a dark current component flowing through the conversion layer included in the voltage signal, the temperature of the conversion layer is determined. And a conversion layer temperature calculation unit to be obtained.
　この発明の光または放射線撮像装置によれば、変換層において光または放射線から変換された電荷信号は、２次元マトリックス状に分割された検出素子ごとに読みだされ、電荷電圧変換手段により電圧信号へ変換される。この電圧信号を構成する成分において、変換層に流れる暗電流成分を基に、変換層の温度を測定することができる。 According to the light or radiation imaging apparatus of the present invention, the charge signal converted from light or radiation in the conversion layer is read for each detection element divided into a two-dimensional matrix and converted into a voltage signal by the charge-voltage conversion means. Converted. Among the components constituting this voltage signal, the temperature of the conversion layer can be measured based on the dark current component flowing in the conversion layer.
　変換層温度算出部は、電圧信号内の変換層を流れる暗電流成分と温度との関係式より変換層の温度を求めることができる。これより、変換層の正確な温度を測定することができる。また、変換層温度算出部は、電圧信号内の変換層を流れる暗電流成分と温度との対応表により、変換層の温度を求めることもできる。これより、変換層の温度の測定を高速にすることができる。 The conversion layer temperature calculation unit can obtain the temperature of the conversion layer from the relational expression between the dark current component flowing through the conversion layer in the voltage signal and the temperature. Thereby, the exact temperature of the conversion layer can be measured. Moreover, the conversion layer temperature calculation part can also obtain | require the temperature of a conversion layer from the correspondence table of the dark current component which flows through the conversion layer in a voltage signal, and temperature. As a result, the temperature of the conversion layer can be measured at high speed.
　また、変換層は主画素領域と補正用画素領域に分けられ、主画素領域内の変換層における２次元温度分布を算出する温度分布算出部を備えることで、補正用画素領域の変換層の温度から、主画素領域の変換層の温度分布を測定することができる。これより、主画素領域の変換層の温度を、主画素領域内の検出素子から読み出された電圧信号から求める必要がないので高速に２次元温度分布を測定することができる。主画素領域をさらに複数の検出画素領域に分ければ、検出画素領域ごとの２次元温度分布を測定することもできる。これより、検出素子ごとの２次元温度分布を測定するよりも高速に温度分布を測定することができる。 The conversion layer is divided into a main pixel region and a correction pixel region, and includes a temperature distribution calculation unit that calculates a two-dimensional temperature distribution in the conversion layer in the main pixel region, so that the temperature of the conversion layer in the correction pixel region Thus, the temperature distribution of the conversion layer in the main pixel region can be measured. As a result, it is not necessary to obtain the temperature of the conversion layer in the main pixel region from the voltage signal read from the detection element in the main pixel region, so that the two-dimensional temperature distribution can be measured at high speed. If the main pixel region is further divided into a plurality of detection pixel regions, the two-dimensional temperature distribution for each detection pixel region can also be measured. Thus, the temperature distribution can be measured at a higher speed than the measurement of the two-dimensional temperature distribution for each detection element.
　また、変換層の２次元温度分布から、検出素子ごとの電圧信号における暗電流成分を求める暗電流成分算出部と、温度に非変動なアンプノイズを除去するアンプノイズ除去部と、
温度に対して変動する暗電流成分をアンプノイズが除去された電圧信号からさらに除去する暗電流成分除去部とを備えることで、ノイズが除去された光または放射線検出信号を得ることができる。 In addition, a dark current component calculation unit that obtains a dark current component in a voltage signal for each detection element from a two-dimensional temperature distribution of the conversion layer, an amplifier noise removal unit that removes amplifier noise that does not vary with temperature,
By providing a dark current component removing unit that further removes a dark current component that fluctuates with respect to temperature from a voltage signal from which amplifier noise has been removed, a light or radiation detection signal from which noise has been removed can be obtained.
　また、補正用画素領域については、変換層の片端に配置されていてもよいし、変換層の両端に配置されているものでもよいし、変換層の四辺に沿って端部に配置されているものでもよい。変換層の材料として、ＣｄＴｅまたはＣｄＺｎＴｅ（テルル化カドミウム亜鉛）でもよいし、ａ－Ｓｅでもよい。変換層の材料がＣｄＴｅまたはＣｄＺｎＴｅであれば、温度変動する暗電流によるノイズを除去することができる光または放射線撮像装置を提供することができる。また、変換層の材料がａ－Ｓｅであれば、変換層の温度を正確に測定することができるので結晶化を防ぐことができる光または放射線撮像装置を提供することができる。 The correction pixel region may be disposed at one end of the conversion layer, may be disposed at both ends of the conversion layer, or is disposed at the end along the four sides of the conversion layer. It may be a thing. The material of the conversion layer may be CdTe or CdZnTe (cadmium zinc telluride) or a-Se. If the material of the conversion layer is CdTe or CdZnTe, it is possible to provide a light or radiation imaging apparatus capable of removing noise due to dark current that fluctuates in temperature. Further, if the material of the conversion layer is a-Se, the temperature of the conversion layer can be accurately measured, so that a light or radiation imaging apparatus that can prevent crystallization can be provided.
　この発明に係る光または放射線撮像装置によれば、光または放射線に感応する変換層の温度状況を精度よく測定することができる光または放射線撮像装置を提供することができる。 The light or radiation imaging apparatus according to the present invention can provide a light or radiation imaging apparatus that can accurately measure the temperature state of the conversion layer sensitive to light or radiation.
実施例に係るＸ線撮像装置の全体構成を示すブロック図である。It is a block diagram which shows the whole structure of the X-ray imaging device which concerns on an Example. 実施例に係るＸ線撮像装置に備わるＸ線平面検出器の構成を示すブロック図である。It is a block diagram which shows the structure of the X-ray plane detector with which the X-ray imaging device which concerns on an Example is equipped. 実施例に係るＸ線撮像装置に備わるＸ線平面検出器のＸ線変換層周辺部の概略縦断面図である。It is a schematic longitudinal cross-sectional view of the X-ray conversion layer periphery part of the X-ray plane detector with which the X-ray imaging device which concerns on an Example is equipped. 実施例に係る電荷電圧変換部の構成を示す回路図である。It is a circuit diagram which shows the structure of the charge voltage converter which concerns on an Example. 実施例に係る電圧信号の暗電流成分およびアンプノイズ成分と温度との関係を示すグラフ図である。It is a graph which shows the relationship between the dark current component of the voltage signal which concerns on an Example, an amplifier noise component, and temperature. 実施例に係る電圧信号のノイズ成分と温度との関係を示すグラフ図である。It is a graph which shows the relationship between the noise component of the voltage signal which concerns on an Example, and temperature. 本発明の他の実施形態に係るＸ線平面検出器の構成を示すブロック図である。It is a block diagram which shows the structure of the X-ray flat panel detector which concerns on other embodiment of this invention. 本発明の他の実施形態に係るＸ線平面検出器の構成を示すブロック図である。It is a block diagram which shows the structure of the X-ray flat panel detector which concerns on other embodiment of this invention. 本発明の他の実施形態に係るＸ線平面検出器の構成を示すブロック図である。It is a block diagram which shows the structure of the X-ray flat panel detector which concerns on other embodiment of this invention.
　１　…　Ｘ線管
　３、３３、３４　…　Ｘ線平面検出器（ＦＰＤ）
　４　…　Ａ／Ｄ変換器
　５　…　画像処理部
　２３　…　画像メモリ部
　２４　…　アンプノイズ除去部
　２５　…　温度変動ノイズ処理部
　２６　…　画像構成部
　２７　…　変換層温度算出部
　２８　…　変換層温度分布算出部
　２９　…　温度変動ノイズ算出部
　３０　…　温度変動ノイズ除去部
　ＤＵ　…　Ｘ線検出素子
　ＸＤ１～ＸＤ４　…　Ｘ線検出部
　Ａ１、Ａ１１、Ａ１２、Ａ１３　…　主画素領域
　Ａ２～Ａ１０　…　検出画素領域
　Ｂ１～Ｂ６　…　補正用画素領域
　ＧＬ１～ＧＬ１０　…　ゲート線
　ＤＬ１～ＤＬ１０　…　データ線 DESCRIPTION OF SYMBOLS 1 ... X-ray tube 3, 33, 34 ... X-ray plane detector (FPD)
DESCRIPTION OF SYMBOLS 4 ... A / D converter 5 ... Image processing part 23 ... Image memory part 24 ... Amplifier noise removal part 25 ... Temperature fluctuation noise processing part 26 ... Image structure part 27 ... Conversion layer temperature calculation part 28 ... Conversion layer temperature distribution calculation part 29 ... Temperature fluctuation noise calculation section 30 ... Temperature fluctuation noise elimination section DU ... X-ray detection elements XD1 to XD4 ... X-ray detection sections A1, A11, A12, A13 ... Main pixel areas A2 to A10 ... Detection pixel areas B1 to B6 ... Correction pixel region GL1 to GL10 ... Gate line DL1 to DL10 ... Data line
　以下、図面を参照してこの発明の実施例を説明する。
　図１は実施例に係るＸ線撮像装置の全体構成を示すブロック図であり、図２はＸ線撮像装置に備わるＸ線平面検出器の構成を示すブロック図であり、図３はＸ線平面検出器のＸ線変換層周辺の概略縦断面図であり、図４は電荷電圧変換部の構成を示す回路図である。本実施例では、入射する光または放射線としてＸ線を例に採って説明するとともに、放射線撮像装置としてＸ線撮像装置を例に採って説明する。 Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram illustrating an overall configuration of an X-ray imaging apparatus according to an embodiment, FIG. 2 is a block diagram illustrating a configuration of an X-ray flat panel detector included in the X-ray imaging apparatus, and FIG. 3 is an X-ray plane. FIG. 4 is a schematic longitudinal sectional view around the X-ray conversion layer of the detector, and FIG. 4 is a circuit diagram showing the configuration of the charge-voltage converter. In the present embodiment, X-rays will be described as an example of incident light or radiation, and an X-ray imaging apparatus will be described as an example of a radiation imaging apparatus.
　＜Ｘ線撮像装置＞
　本実施例に係るＸ線撮像装置は、被検体にＸ線を照射して撮像を行う。具体的には、被検体を透過したＸ線像がＸ線変換層上に投影されて、像の濃淡に比例した電荷信号（キャリア）がＸ線変換層内に発生する。 <X-ray imaging device>
The X-ray imaging apparatus according to the present embodiment performs imaging by irradiating a subject with X-rays. Specifically, an X-ray image transmitted through the subject is projected on the X-ray conversion layer, and a charge signal (carrier) proportional to the density of the image is generated in the X-ray conversion layer.
　図１に示すように、Ｘ線撮像装置は、撮像対象である被検体ＭにＸ線を照射するＸ線管１と、被検体Ｍを載置させる天板２と、被検体Ｍを透過したＸ線量に応じた電荷信号に変換（Ｘ線を電荷信号として検出）し、さらに、この電荷信号を電圧信号に変換して出力するＸ線平面検出器（以下、ＦＰＤと称す）３と、ＦＰＤ３から出力された電圧信号をアナログからデジタルへ変換するＡ／Ｄ変換器４と、Ａ／Ｄ変換器４で変換されたデジタルの電圧信号を処理してＸ線透視画像を構成する画像処理部５と、Ｘ線撮像に関する種々の制御を行う主制御部６と、主制御部６での制御に基づいて管電圧や管電流を発生させＸ線管１を制御するＸ線管制御部７と、透視撮像に関する入力設定を行うことが可能な入力部８と、画像処理部５で処理されて得られたＸ線画像などを表示する表示部９と、画像処理部５で処理されて得られたＸ線透視画像などを記憶する記憶部１０などを備えている。さらに、Ｘ線撮像装置の各部構成を詳細に説明する。 As shown in FIG. 1, the X-ray imaging apparatus transmits an X-ray tube 1 that irradiates a subject M to be imaged with X-rays, a top plate 2 on which the subject M is placed, and the subject M. An X-ray flat panel detector (hereinafter referred to as FPD) 3 for converting into a charge signal corresponding to the X-ray dose (detecting the X-ray as a charge signal), and further converting the charge signal into a voltage signal and outputting the voltage signal; A / D converter 4 for converting the voltage signal output from the analog to digital, and an image processing unit 5 for processing the digital voltage signal converted by the A / D converter 4 to construct an X-ray fluoroscopic image A main control unit 6 that performs various controls related to X-ray imaging, an X-ray tube control unit 7 that controls the X-ray tube 1 by generating a tube voltage and a tube current based on the control of the main control unit 6; Processed by the input unit 8 capable of performing input settings relating to fluoroscopic imaging and the image processing unit 5 A display unit 9 for displaying the obtained X-ray image, and a storage unit 10 for storing the X-ray fluoroscopic image obtained is processed by the image processing unit 5. Further, the configuration of each part of the X-ray imaging apparatus will be described in detail.
　図２に示すように、ＦＰＤ３は、複数のＸ線検出素子ＤＵを有するＸ線検出部ＸＤ１、ゲート駆動回路１１、電荷電圧変換部１２、サンプル・ホールド部１３、マルチプレクサ１４とが備えられている。これら複数のＸ線検出素子ＤＵはゲート線ＧＬ１～ＧＬ１０によりゲート駆動回路１１と接続されつつ、データ線ＤＬ１～ＤＬ１０により電荷電圧変換部１２と接続されている。Ｘ線検出素子ＤＵは本発明における検出素子に相当し、電荷電圧変換部１２は本発明における電荷電圧変換手段に相当する。 As shown in FIG. 2, the FPD 3 includes an X-ray detection unit XD1 having a plurality of X-ray detection elements DU, a gate drive circuit 11, a charge voltage conversion unit 12, a sample and hold unit 13, and a multiplexer 14. . The plurality of X-ray detection elements DU are connected to the gate drive circuit 11 by gate lines GL1 to GL10, and are connected to the charge / voltage converter 12 by data lines DL1 to DL10. The X-ray detection element DU corresponds to the detection element in the present invention, and the charge voltage conversion unit 12 corresponds to the charge voltage conversion means in the present invention.
　Ｘ線検出素子ＤＵは、入射されたＸ線に感応して電荷信号を出力するものであり、Ｘ線が入射されるＸ線検出部ＸＤ１に縦横の２次元マトリックス状に配列されている。なお、図２においては、Ｘ線検出素子ＤＵが縦１０×横１０の２次元マトリックス状に配列したものを一例として図示しているが、実際のＸ線検出部ＸＤ１にはＸ線検出素子ＤＵが、例えば、縦４０９６×横４０９６程度に２次元マトリックス状に配列されて用いられる。 The X-ray detection elements DU output charge signals in response to incident X-rays, and are arranged in a vertical and horizontal two-dimensional matrix form on the X-ray detection unit XD1 where X-rays are incident. In FIG. 2, the X-ray detection elements DU arranged in a two-dimensional matrix of 10 × 10 are shown as an example. However, the actual X-ray detection unit XD1 includes the X-ray detection elements DU. Are used, for example, arranged in a two-dimensional matrix in a length of about 4096 × width 4096.
　ＦＰＤ３内のＸ線検出部ＸＤ１は主画素領域Ａ１と補正用画素領域Ｂ１とに分けられる。本実施例では、補正用画素領域Ｂ１はＸ線検出部ＸＤ１の左端に配置されている。主画素領域Ａ１に配置されているＸ線検出素子ＤＵは、被検体Ｍを透過した放射線量を測定するためのものであり、補正用画素領域Ｂ１に配置されているＸ線検出素子ＤＵはＸ線検出部ＸＤ１内のＸ線変換層の温度を測定するためのものである。補正用画素領域Ｂ１のＸ線検出素子ＤＵ上には、Ｘ線の入射を防ぐ鉛シール等が貼付けられている。 The X-ray detection part XD1 in the FPD 3 is divided into a main pixel area A1 and a correction pixel area B1. In the present embodiment, the correction pixel region B1 is disposed at the left end of the X-ray detection unit XD1. The X-ray detection element DU arranged in the main pixel area A1 is for measuring the amount of radiation transmitted through the subject M, and the X-ray detection element DU arranged in the correction pixel area B1 is X This is for measuring the temperature of the X-ray conversion layer in the line detector XD1. On the X-ray detection element DU in the correction pixel region B1, a lead seal or the like for preventing X-ray incidence is attached.
　また、Ｘ線検出素子ＤＵは図３に示すように、高電圧のバイアス電圧Ｖａを印加する電圧印加電極１６と、入射したＸ線から電荷信号へ変換するＸ線変換層１７とＸ線変換層１７で変換された電荷信号を蓄積、読み出し（出力）を行うアクティブマトリックス基板１８とを備えている。このように、Ｘ線変換層１７をＸ線検出素子ＤＵが２次元マトリックス状に分割してＸ線を検出している。アクティブマトリックス基板１８は本発明における読み出し手段に相当する。 As shown in FIG. 3, the X-ray detection element DU includes a voltage application electrode 16 that applies a high bias voltage Va, an X-ray conversion layer 17 that converts an incident X-ray into a charge signal, and an X-ray conversion layer. And an active matrix substrate 18 for accumulating and reading out (outputting) the charge signal converted at 17. Thus, the X-ray conversion layer 17 is divided by the X-ray detection elements DU into a two-dimensional matrix to detect X-rays. The active matrix substrate 18 corresponds to the reading means in the present invention.
　Ｘ線変換層１７は、Ｘ線感応型半導体からなり、例えば、非晶質のａ－Ｓｅまたは多結晶化合物のＣｄＴｅまたはＣｄＺｎＴｅで形成されている。また、Ｘ線変換層１７にＸ線が入射すると、このＸ線のエネルギーに比例した所定個数のキャリア（電荷信号）が直接生成される構成（直接変換型）となっている。また、生成された電荷信号は、電圧印加電極１６にバイアス電圧Ｖａが印加されたことに基づいて、画素電極２０ごとに収集される。 The X-ray conversion layer 17 is made of an X-ray sensitive semiconductor and is made of, for example, amorphous a-Se or a polycrystalline compound CdTe or CdZnTe. Further, when X-rays are incident on the X-ray conversion layer 17, a predetermined number of carriers (charge signals) proportional to the energy of the X-rays are directly generated (direct conversion type). Further, the generated charge signal is collected for each pixel electrode 20 based on the application of the bias voltage Va to the voltage application electrode 16.
　アクティブマトリックス基板１８は図３に示すように、絶縁性のガラス基板１９が設けられ、このガラス基板１９上には、画素電極２０ごとに収集された電荷信号を蓄積するコンデンサＣａ、スイッチング素子としての薄膜トランジスタ（以下ＴＦＴと称す）２１、ゲート駆動回路１１からＴＦＴ２１を制御するためのゲート線ＧＬ１～ＧＬ１０、ＴＦＴ２１から電荷信号が読み出されるデータ線ＤＬ１～ＤＬ１０とを設けている。 As shown in FIG. 3, the active matrix substrate 18 is provided with an insulating glass substrate 19, on which a capacitor Ca that accumulates a charge signal collected for each pixel electrode 20 and a switching element. A thin film transistor (hereinafter referred to as TFT) 21, gate lines GL 1 to GL 10 for controlling the TFT 21 from the gate driving circuit 11, and data lines DL 1 to DL 10 for reading out charge signals from the TFT 21 are provided.
　次に、ゲート駆動回路１１は、Ｘ線検出素子ＤＵで検出された電荷信号を順次選択的に取り出すために、各Ｘ線検出素子ＤＵのＴＦＴ２１を動作させるものである。ゲート駆動回路１１は、Ｘ線検出素子ＤＵの横行ごとに共通して接続されるゲート線ＧＬ１～ＧＬ１０を順次選択してゲート信号を送る。この選択した行内のＸ線検出素子ＤＵのＴＦＴ２１は、ゲート信号により一斉にスイッチオン状態になり、コンデンサＣａに蓄積された電荷信号がデータ線ＤＬ１～ＤＬ１０を通り電荷電圧変換部１２に出力される。 Next, the gate drive circuit 11 operates the TFT 21 of each X-ray detection element DU in order to selectively extract the charge signals detected by the X-ray detection elements DU. The gate drive circuit 11 sequentially selects the gate lines GL1 to GL10 connected in common for each row of the X-ray detection elements DU and sends a gate signal. The TFTs 21 of the X-ray detection elements DU in the selected row are simultaneously switched on by the gate signal, and the charge signal stored in the capacitor Ca is output to the charge / voltage conversion unit 12 through the data lines DL1 to DL10. .
　次に、電荷電圧変換部１２には、Ｘ線検出素子ＤＵの縦列ごとのデータ線ＤＬ１～ＤＬ１０に対応した数（図２では１０個）の図４に示すような電荷電圧変換アンプ２２が備えられている。電荷電圧変換アンプ２２は、各Ｘ線検出素子ＤＵから出力された電荷信号を電圧信号に変換する電荷検出増幅回路（ＣＳＡ：Charge Sensitive Amplifier）である。電荷電圧変換アンプ２２にて、データ線ＤＬ１～ＤＬ１０から読み込まれた電荷信号を電圧信号に変換し、サンプル・ホールド部１３に出力する。電荷電圧変換部１２は、本発明における電荷電圧変換手段に相当する。 Next, the charge-voltage conversion unit 12 includes a number of charge-voltage conversion amplifiers 22 as shown in FIG. 4 corresponding to the data lines DL1 to DL10 for each column of the X-ray detection elements DU (10 in FIG. 2). It has been. The charge-voltage conversion amplifier 22 is a charge detection amplification circuit (CSA: Charge Sensitive Amplifier) that converts a charge signal output from each X-ray detection element DU into a voltage signal. The charge voltage conversion amplifier 22 converts the charge signals read from the data lines DL1 to DL10 into voltage signals and outputs them to the sample and hold unit 13. The charge voltage conversion unit 12 corresponds to the charge voltage conversion means in the present invention.
　次に、サンプル・ホールド部１３は、電荷電圧変換アンプ２２の数に対応した数のサンプルホールド回路が設けられている。サンプルホールド回路は、電荷電圧変換アンプ２２から出力された電圧信号を予め定められた一定時間においてサンプリングする。次に、予め定められた一定時間が経過した時点での電圧信号を保持（ホールド）し、安定した状態の電圧信号をマルチプレクサ１４に出力する。 Next, the sample and hold unit 13 is provided with a number of sample and hold circuits corresponding to the number of charge-voltage conversion amplifiers 22. The sample and hold circuit samples the voltage signal output from the charge-voltage conversion amplifier 22 at a predetermined time. Next, the voltage signal at the time when a predetermined time has elapsed is held (held), and the voltage signal in a stable state is output to the multiplexer 14.
　次に、マルチプレクサ１４の内部には、サンプルホールド回路の数に対応した数のスイッチが設けられている。スイッチのいずれかひとつを順次ＯＮ状態に切り替えて、各サンプルホールド回路から出力される電圧信号の一つずつを束ねた時分割信号として、Ａ／Ｄ変換器４へ出力する。Ａ／Ｄ変換器４は、マルチプレクサ１４からの電圧信号について、予め定められたタイミングでサンプリングしてデジタルの電圧信号に変換し、画像処理部５に出力する。 Next, the number of switches corresponding to the number of sample and hold circuits is provided inside the multiplexer 14. Any one of the switches is sequentially switched to the ON state, and is output to the A / D converter 4 as a time division signal obtained by bundling one voltage signal output from each sample hold circuit. The A / D converter 4 samples the voltage signal from the multiplexer 14 at a predetermined timing, converts it to a digital voltage signal, and outputs it to the image processing unit 5.
　＜画像処理部＞
　画像処理部５の内部には、図１に示すように、画像メモリ部２３と、アンプノイズ除去部２４と、温度変動ノイズ処理部２５と、画像構成部２６とを備えている。温度変動ノイズ処理部２５内には、さらに、変換層温度算出部２７と、変換層温度分布算出部２８と、温度変動ノイズ算出部２９と、温度変動ノイズ除去部３０とを設けている。画像処理部５では、ＦＰＤ３からＡ／Ｄ変換器４を介して転送された電圧信号からアンプノイズおよび温度変動ノイズを除去してＸ線透視画像を構成する。 <Image processing unit>
As shown in FIG. 1, the image processing unit 5 includes an image memory unit 23, an amplifier noise removing unit 24, a temperature fluctuation noise processing unit 25, and an image configuration unit 26. In the temperature variation noise processing unit 25, a conversion layer temperature calculation unit 27, a conversion layer temperature distribution calculation unit 28, a temperature variation noise calculation unit 29, and a temperature variation noise removal unit 30 are further provided. The image processing unit 5 removes amplifier noise and temperature fluctuation noise from the voltage signal transferred from the FPD 3 via the A / D converter 4 to form an X-ray fluoroscopic image.
　まず、画像処理部５に転送される電圧信号がどのような信号であるかを説明する。画像処理部５に転送される電圧信号（以下、検出電圧信号と称す）は、その発生する原因によって３つの成分に分けることができる。つまり、検出電圧信号は、Ｘ線透過画像信号と温度変動ノイズＮｔと温度非変動ノイズ３２とにより構成される。
　（検出電圧信号）＝（Ｘ線透過画像信号）＋（温度変動ノイズ）＋（温度非変動ノイズ） First, what kind of signal the voltage signal transferred to the image processing unit 5 is will be described. A voltage signal transferred to the image processing unit 5 (hereinafter referred to as a detection voltage signal) can be divided into three components depending on the cause of the voltage signal. That is, the detection voltage signal is composed of the X-ray transmission image signal, the temperature variation noise Nt, and the temperature non-variation noise 32.
(Detection voltage signal) = (X-ray transmission image signal) + (Temperature fluctuation noise) + (Temperature non-fluctuation noise)
　Ｘ線透過画像信号とは、被検体Ｍを透過したＸ線がＸ線変換層１７により変換された電荷信号による電圧信号であり、Ｘ線透視画像を再構成するのに必要な電圧信号である。 The X-ray transmission image signal is a voltage signal based on a charge signal obtained by converting the X-ray transmitted through the subject M by the X-ray conversion layer 17 and is a voltage signal necessary for reconstructing the X-ray fluoroscopic image. .
　温度変動ノイズＮｔとは、Ｘ線変換層１７内を流れる暗電流が電圧信号として変換されたノイズ信号であり、Ｘ線変換層１７の温度により敏感にその値が変動する。温度変動ノイズＮｔは一般に以下の式で表すことができる。 The temperature fluctuation noise Nt is a noise signal obtained by converting the dark current flowing in the X-ray conversion layer 17 as a voltage signal, and its value varies sensitively depending on the temperature of the X-ray conversion layer 17. The temperature fluctuation noise Nt can be generally expressed by the following equation.
　Ｎｔ＝α（ｅｘｐ（β／Ｔ）－１）、（α、β：定数、Ｔ：絶対温度［Ｋ］）…（１） Nt = α (exp (β / T) −1), (α, β: constant, T: absolute temperature [K]) (1)
　温度非変動ノイズ３２とは、ＦＰＤ３の使用される温度状況に影響され無い常に略一定のノイズ信号である。この温度非変動ノイズ３２は、電荷電圧変換部１２におけるアンプのオフセットなどにより生じるノイズ信号である。 The temperature non-varying noise 32 is a noise signal that is always substantially constant and is not affected by the temperature condition in which the FPD 3 is used. The temperature non-variation noise 32 is a noise signal generated due to an amplifier offset in the charge-voltage conversion unit 12.
　温度変動ノイズＮｔと温度非変動ノイズ３２は共にＸ線透過画像信号のダイナミックレンジを縮小させるものである。また、Ｘ線撮像装置の設置される環境の温度は空調をしているといえども常に変化しており、温度変動ノイズＮｔが温度変化によりＸ線透視画像上に現れると正確なＸ線透視画像を得ることができない。図５は、温度変動ノイズＮｔと温度非変動ノイズ３２を図示したものである。温度変動ノイズＮｔは暗電流の性質上温度Ｔに対して指数関数的に変動する。 Both the temperature fluctuation noise Nt and the temperature non-variation noise 32 reduce the dynamic range of the X-ray transmission image signal. Further, the temperature of the environment in which the X-ray imaging apparatus is installed is constantly changing even if air conditioning is performed. When the temperature fluctuation noise Nt appears on the X-ray fluoroscopic image due to temperature change, an accurate X-ray fluoroscopic image is displayed. Can't get. FIG. 5 illustrates the temperature fluctuation noise Nt and the temperature non-variation noise 32. The temperature fluctuation noise Nt varies exponentially with respect to the temperature T due to the nature of dark current.
　また、Ｘ線管１からＸ線を照射しない時に得られる暗画像電圧信号は２つの成分に分けることができる。
　（暗画像電圧信号）＝（温度変動ノイズ）＋（温度非変動ノイズ）
これより、検出電圧信号は条件によっては２つの成分にて構成することもできる。
　（検出電圧信号）＝（Ｘ線透過画像信号）＋（暗画像電圧信号）、（但し、温度一定）
　このように、Ｘ線透過撮像時と暗画像撮像時とのＸ線変換層１７の温度が同一の場合にのみ、上式は成立する。 Further, the dark image voltage signal obtained when the X-ray tube 1 does not irradiate X-rays can be divided into two components.
(Dark image voltage signal) = (Temperature fluctuation noise) + (Temperature non-variation noise)
Thus, the detection voltage signal can be composed of two components depending on conditions.
(Detection voltage signal) = (X-ray transmission image signal) + (dark image voltage signal) (however, temperature is constant)
As described above, the above formula is established only when the temperature of the X-ray conversion layer 17 is the same between the X-ray transmission imaging and the dark image imaging.
　温度非変動ノイズ３２の電圧信号値をγとすると、γは温度によらず略一定値であるから、暗画像電圧信号Ｄは以下の式で表すことができる。 When the voltage signal value of the temperature non-variable noise 32 is γ, γ is a substantially constant value regardless of the temperature, and therefore the dark image voltage signal D can be expressed by the following equation.
　Ｄ＝α（ｅｘｐ（β／Ｔ）－１）＋γ、（γ：定数）…（２） D = α (exp (β / T) -1) + γ, (γ: constant) (2)
　（１）および（２）式のαとβの値は、Ｘ線変換層１７の構成物質および構成状態により変動する値であり、γは温度によらず略一定であるので、ＦＰＤ３の使用する温度を変化させながら暗画像時の暗画像電圧信号を測定することで３つの定数α、β、γを求めることができる。 The values of α and β in the formulas (1) and (2) are values that vary depending on the constituent material and the constituent state of the X-ray conversion layer 17, and γ is substantially constant regardless of the temperature. Three constants α, β, and γ can be obtained by measuring the dark image voltage signal during dark images while changing the temperature.
　図６に示すように、Ｘ線変換層１７の温度Ｔ１、Ｔ２、Ｔ３の各点における暗画像電圧信号の値を測定することで（２）式の３つの定数α、β、γの値を求める。これより、暗画像電圧信号の値から温度変動ノイズＮｔの近似式を求めることができる。温度と暗画像電圧信号との測定を３点に限らず、測定点を増やせば増やすほど精度の良い近似式を求めることができる。 As shown in FIG. 6, the values of the three constants α, β, and γ in the equation (2) are obtained by measuring the values of the dark image voltage signals at the points of the temperatures T1, T2, and T3 of the X-ray conversion layer 17. Ask. Thus, an approximate expression of the temperature fluctuation noise Nt can be obtained from the value of the dark image voltage signal. The measurement of the temperature and the dark image voltage signal is not limited to three points, and as the number of measurement points is increased, a more accurate approximate expression can be obtained.
　このとき、ＦＰＤ３の設置されている環境温度を正確にＴ１、Ｔ２、Ｔ３と３つの温度設定をした場合の暗画像電圧信号を測定してもよいし、Ｘ線変換層１７の温度を正確に測定し、異なる３つの温度Ｔ１、Ｔ２、Ｔ３の場合の暗画像電圧信号を測定してもよい。また、温度変動ノイズＮｔの特性曲線を３点以上の温度において測定した暗画像電圧信号の値から、温度と温度変動ノイズＮｔとのルックアップテーブルを作成してもよい。このようにして、Ｘ線検出素子ＤＵごとの温度と温度変動ノイズとの近似式またはルックアップテーブルを作成することができる。この近似式は本発明における関係式に相当し、ルックアップテーブルは本発明における対応表に相当する。 At this time, the dark image voltage signal may be measured when the environmental temperature where the FPD 3 is installed is accurately set to T1, T2, and T3, and the temperature of the X-ray conversion layer 17 may be accurately measured. The dark image voltage signal at three different temperatures T1, T2, and T3 may be measured. Alternatively, a look-up table of temperature and temperature fluctuation noise Nt may be created from values of dark image voltage signals obtained by measuring characteristic curves of temperature fluctuation noise Nt at three or more temperatures. In this way, an approximate expression or a look-up table between the temperature and the temperature fluctuation noise for each X-ray detection element DU can be created. This approximate expression corresponds to the relational expression in the present invention, and the lookup table corresponds to the correspondence table in the present invention.
　次に、検出電圧信号からＸ線透過画像信号を求める画像処理部５の各構成部の説明をする。 Next, each component of the image processing unit 5 that obtains an X-ray transmission image signal from the detection voltage signal will be described.
　Ａ／Ｄ変換器４から出力されたデジタルの電圧信号は画像メモリ部２３に一時的に記憶される。また、後で説明するように、検出電圧信号から温度非変動ノイズ成分γが除去された電圧信号も一時的に記憶される。 The digital voltage signal output from the A / D converter 4 is temporarily stored in the image memory unit 23. Further, as will be described later, a voltage signal obtained by removing the temperature non-varying noise component γ from the detected voltage signal is also temporarily stored.
　アンプノイズ除去部２４には予め温度非変動ノイズ成分であるγ値が格納されており、検出電圧信号から温度非変動ノイズ成分γを除去する。温度非変動ノイズ成分γが除去された検出電圧信号の値は、画像メモリ部２３へ再び格納される。また、検出電圧信号が暗画像電圧信号の場合、温度非変動ノイズ成分γが除去された暗画像電圧信号の値は、Ｘ線変換層１７の温度を測定するために変換層温度算出部２７へ送られる。 The amplifier noise removal unit 24 stores a γ value that is a temperature non-variable noise component in advance, and removes the temperature non-variable noise component γ from the detected voltage signal. The value of the detection voltage signal from which the temperature non-variation noise component γ has been removed is stored again in the image memory unit 23. When the detected voltage signal is a dark image voltage signal, the value of the dark image voltage signal from which the temperature non-varying noise component γ is removed is sent to the conversion layer temperature calculation unit 27 in order to measure the temperature of the X-ray conversion layer 17. Sent.
　変換層温度算出部２７には、温度変換近似式またはルックアップテーブルが備えられており、暗画像電圧信号から温度非変動ノイズ成分γが除去された電圧信号から、Ｘ線変換層１７の温度を算出する。この算出された温度は主制御部６にも転送され、規定の温度よりも高い場合は、表示部９にて警告を発することもできる。また、緊急的処置として、主制御部６からの指令により、ＦＰＤ３への電源供給をカットしたり、別に備えた冷却装置にてＦＰＤ３を冷却してもよい。 The conversion layer temperature calculation unit 27 includes a temperature conversion approximate expression or a lookup table, and calculates the temperature of the X-ray conversion layer 17 from the voltage signal obtained by removing the temperature non-varying noise component γ from the dark image voltage signal. calculate. The calculated temperature is also transferred to the main control unit 6, and when the temperature is higher than the specified temperature, a warning can be issued on the display unit 9. Further, as an emergency measure, the power supply to the FPD 3 may be cut or the FPD 3 may be cooled by a separate cooling device according to a command from the main control unit 6.
　変換層温度分布算出部２８には、Ｘ線検出部ＸＤ１に設けられた全てのＸ線検出画素ＤＵの温度分布特性が関数またはルックアップテーブルとして備えられている。ある特定のＸ線検出素子ＤＵのＸ線変換層１７の温度がわかれば、Ｘ線検出部ＸＤ１に設けられた全てのＸ線検出素子ＤＵ内のＸ線変換層１７の温度分布特性を算出することができる。 The conversion layer temperature distribution calculation unit 28 includes temperature distribution characteristics of all X-ray detection pixels DU provided in the X-ray detection unit XD1 as a function or a lookup table. If the temperature of the X-ray conversion layer 17 of a specific X-ray detection element DU is known, the temperature distribution characteristics of the X-ray conversion layers 17 in all the X-ray detection elements DU provided in the X-ray detection unit XD1 are calculated. be able to.
　温度変動ノイズ算出部２９では、算出された各Ｘ線検出素子ＤＵ内のＸ線変換層１７の温度から、それぞれのＸ線検出素子ＤＵに発生する温度変動ノイズＮｔを算出する。温度変動ノイズ算出部２９には、予め作成された各Ｘ線検出素子ＤＵの温度変動ノイズＮｔの近似式またはルックアップテーブルが備えられており、これより温度変動ノイズＮｔを算出する。 The temperature fluctuation noise calculation unit 29 calculates the temperature fluctuation noise Nt generated in each X-ray detection element DU from the calculated temperature of the X-ray conversion layer 17 in each X-ray detection element DU. The temperature fluctuation noise calculation unit 29 is provided with an approximate expression or look-up table of the temperature fluctuation noise Nt of each X-ray detection element DU created in advance, and calculates the temperature fluctuation noise Nt from this.
　温度変動ノイズ除去部３０では、各Ｘ線検出素子ＤＵの検出電圧信号から温度非変動ノイズ３１が除去された電圧信号より、それぞれ対応する温度変動ノイズＮｔを除去することで、Ｘ線検出素子ＤＵごとのＸ線透過画像信号を得ることができる。 The temperature fluctuation noise removing unit 30 removes the corresponding temperature fluctuation noise Nt from the voltage signal from which the temperature non-variation noise 31 has been removed from the detection voltage signal of each X-ray detection element DU, whereby the X-ray detection element DU. X-ray transmission image signals for each can be obtained.
　画像構成部２６では、Ｘ線透過画像信号よりＸ線透視画像を構成する。また、Ｘ線透視画像に限らず、ＣＴ撮像時には断層像を再構成することもできる。構成されたＸ線透視画像は、主制御部６に転送され、表示部９で表示されるか、記憶部１０にて格納される。 The image construction unit 26 constructs an X-ray fluoroscopic image from the X-ray transmission image signal. In addition to the X-ray fluoroscopic image, a tomographic image can be reconstructed at the time of CT imaging. The configured fluoroscopic image is transferred to the main control unit 6 and displayed on the display unit 9 or stored in the storage unit 10.
　＜Ｘ線撮像＞
　次に、この実施例におけるＸ線撮像装置でＸ線撮像が実行される場合の動作を、図１～図４を用いて説明する。 <X-ray imaging>
Next, an operation when X-ray imaging is executed by the X-ray imaging apparatus in this embodiment will be described with reference to FIGS.
　まず、入力部８でＸ線撮像開始の指示がされると、主制御部６は、Ｘ線管制御部７とＦＰＤ３とを制御する。Ｘ線管制御部７は、主制御部６からの制御に基づいて管電圧や管電流を発生させＸ線管１を制御し、Ｘ線管１からＸ線が被検体Ｍに照射される。さらに、被検体Ｍを透過したＸ線は、ＦＰＤ３のＸ線検出素子ＤＵにより被検体Ｍを透過したＸ線量に応じた電荷信号に変換される。変換された電荷信号は、コンデンサＣａにより蓄積される。 First, when an instruction to start X-ray imaging is given by the input unit 8, the main control unit 6 controls the X-ray tube control unit 7 and the FPD 3. The X-ray tube control unit 7 controls the X-ray tube 1 by generating tube voltage and tube current based on the control from the main control unit 6, and the subject M is irradiated with X-rays from the X-ray tube 1. Further, the X-ray transmitted through the subject M is converted into a charge signal corresponding to the X-ray dose transmitted through the subject M by the X-ray detection element DU of the FPD 3. The converted charge signal is accumulated by the capacitor Ca.
　次に、ゲート駆動回路１１がゲート線を順次選択する。本実施例では、ゲート線Ｇ１，Ｇ２，Ｇ３，…，Ｇ９，Ｇ１０の順に１つずつ選択するものとして説明する。ゲート駆動回路１１がゲート線Ｇ１を選択して、ゲート線Ｇ１に接続された各Ｘ線検出素子ＤＵが指定される。指定された各Ｘ線検出素子ＤＵのＴＦＴ２１のゲートは、ゲート信号が送られることで電圧が印加され、ＯＮ状態となる。これより、指定された各ＴＦＴ２１に接続されるコンデンサＣａに蓄積された電荷信号が、ＴＦＴ２１を経由して、データ線ＤＬ１～ＤＬ１０に読み出される。次に、ゲート駆動回路１１がゲート線Ｇ２を選択して、同様の手順で、ゲート線Ｇ２に接続された各Ｘ線検出素子ＤＵが指定され、その指定された各Ｘ線検出素子ＤＵのコンデンサＣａに蓄積された電荷信号が、データ線ＤＬ１～ＤＬ１０に読み出される。残りのゲート線Ｇ３～Ｇ１０についても同様に順に選択することで、２次元状に電荷信号を読み出す。 Next, the gate drive circuit 11 sequentially selects the gate lines. In this embodiment, description will be made assuming that gate lines G1, G2, G3,..., G9, G10 are selected one by one in order. The gate drive circuit 11 selects the gate line G1, and each X-ray detection element DU connected to the gate line G1 is designated. A voltage is applied to the gate of the TFT 21 of each designated X-ray detection element DU when a gate signal is sent to the ON state. Thus, the charge signal stored in the capacitor Ca connected to each designated TFT 21 is read out to the data lines DL1 to DL10 via the TFT 21. Next, the gate drive circuit 11 selects the gate line G2, and in the same procedure, each X-ray detection element DU connected to the gate line G2 is designated, and the capacitor of each designated X-ray detection element DU is designated. The charge signal stored in Ca is read out to the data lines DL1 to DL10. Similarly, the remaining gate lines G3 to G10 are sequentially selected to read out charge signals in a two-dimensional manner.
　このように、ゲート駆動回路１１がゲート線ＧＬ１～ＧＬ１０を順次選択することで、各ゲート線に接続されたＸ線検出素子ＤＵが指定され、その指定された各Ｘ線検出素子ＤＵのコンデンサＣａに蓄積された電荷信号が、データ線ＤＬ１～ＤＬ１０に読み出される。 In this way, the gate drive circuit 11 sequentially selects the gate lines GL1 to GL10, so that the X-ray detection element DU connected to each gate line is designated, and the capacitor Ca of each designated X-ray detection element DU. The charge signal stored in is read to the data lines DL1 to DL10.
　各データ線に読みだされた電荷信号は電荷電圧変換部１２内の電荷電圧変換アンプ２２において電圧信号へ変換されるとともに増幅される。そして、サンプル・ホールド部１３では、電荷電圧変換部１２にて変換された電圧信号をサンプリングするとともに一旦ホールドする。その後、マルチプレクサ１４からサンプル・ホールド部１３にホールドされた電圧信号を時分割信号として順次出力する。出力された電圧信号は、Ａ／Ｄ変換器４にてアナログ値からデジタル値へ変換される。この変換されたデジタル信号に基づいて、画像処理部５は信号処理を行って、２次元状の撮像画像を構成する。 The charge signal read out to each data line is converted into a voltage signal and amplified by the charge-voltage conversion amplifier 22 in the charge-voltage conversion unit 12. The sample and hold unit 13 samples and holds the voltage signal converted by the charge / voltage conversion unit 12 once. Thereafter, the voltage signal held in the sample and hold unit 13 from the multiplexer 14 is sequentially output as a time division signal. The output voltage signal is converted from an analog value to a digital value by the A / D converter 4. Based on the converted digital signal, the image processing unit 5 performs signal processing to form a two-dimensional captured image.
　＜Ｘ線検出部温度測定＞
　次に、補正用画素領域Ｂ１のＸ線検出素子ＤＵから主画素領域Ａ１のＸ線検出素子ＤＵの温度測定に関して説明する。 <X-ray detector temperature measurement>
Next, temperature measurement from the X-ray detection element DU in the correction pixel area B1 to the X-ray detection element DU in the main pixel area A1 will be described.
　主画素領域Ａ１のＸ線検出素子ＤＵから画像処理部５へ送られた電圧信号を主画素電圧信号とし、補正用画素領域Ｂ１のＸ線検出素子ＤＵから画像処理部５へ送られた電圧信号を補正用電圧信号とする。補正用画素領域Ｂ１はＸ線に対して鉛テープで遮蔽されているので、補正用電圧信号は暗画像電圧信号となる。主画素電圧信号および補正用画素信号は以下の信号成分で構成されている。 A voltage signal sent from the X-ray detection element DU in the main pixel region A1 to the image processing unit 5 is used as a main pixel voltage signal, and a voltage signal sent from the X-ray detection element DU in the correction pixel region B1 to the image processing unit 5 Is a correction voltage signal. Since the correction pixel region B1 is shielded with lead tape against X-rays, the correction voltage signal is a dark image voltage signal. The main pixel voltage signal and the correction pixel signal are composed of the following signal components.
　（主画素電圧信号）＝（Ｘ線透過画像信号）＋（温度変動ノイズ）＋（温度非変動ノイズ） (Main pixel voltage signal) = (X-ray transmission image signal) + (Temperature fluctuation noise) + (Temperature non-variation noise)
　（補正用電圧信号）＝（温度変動ノイズ）＋（温度非変動ノイズ） (Correction voltage signal) = (temperature fluctuation noise) + (temperature non-fluctuation noise)
　画像処理部５へ送られた主画素電圧信号と補正用電圧信号とは画像メモリ部２３に保管されるとともに、アンプノイズ除去部２４へ転送される。アンプノイズ除去部２４では、転送された主画素電圧信号と補正用電圧信号とから予め格納されている温度非変動ノイズ成分γを除去する。この後、温度非変動ノイズ成分γを除去した主画素電圧信号は再び画像メモリ部２３へ保管し、温度非変動ノイズ成分γを除去した補正用電圧信号は、変換層温度算出部２７へ転送する。 The main pixel voltage signal and the correction voltage signal sent to the image processing unit 5 are stored in the image memory unit 23 and transferred to the amplifier noise removing unit 24. The amplifier noise removing unit 24 removes the temperature non-varying noise component γ stored in advance from the transferred main pixel voltage signal and correction voltage signal. Thereafter, the main pixel voltage signal from which the temperature non-varying noise component γ has been removed is stored again in the image memory unit 23, and the correction voltage signal from which the temperature non-varying noise component γ has been removed is transferred to the conversion layer temperature calculating unit 27. .
　変換層温度算出部２７では、温度非変動ノイズ成分γを除去された補正用電圧信号から、補正用画素領域Ｂ１に配置されたＸ線検出素子ＤＵごとのＸ線変換層１７の温度が算出される。そして、この温度データは変換層温度分布算出部２８へ転送される。 The conversion layer temperature calculation unit 27 calculates the temperature of the X-ray conversion layer 17 for each X-ray detection element DU arranged in the correction pixel region B1 from the correction voltage signal from which the temperature non-varying noise component γ is removed. The The temperature data is transferred to the conversion layer temperature distribution calculation unit 28.
　変換層温度分布算出部２８では、転送された補正用画素領域Ｂ１の温度データから主画素領域Ａ１の２次元温度分布が算出される。算出された２次元温度分布データは温度変動ノイズ算出部２９へ転送される。 The conversion layer temperature distribution calculation unit 28 calculates the two-dimensional temperature distribution of the main pixel area A1 from the transferred temperature data of the correction pixel area B1. The calculated two-dimensional temperature distribution data is transferred to the temperature fluctuation noise calculation unit 29.
　温度変動ノイズ算出部２９では、転送された２次元温度分布データより、主画素領域Ａ１の各Ｘ線検出素子ＤＵごとの温度変動ノイズが算出される。各Ｘ線検出素子ＤＵの温度変動ノイズは温度変動ノイズ除去部３０へ転送される。 The temperature fluctuation noise calculation unit 29 calculates temperature fluctuation noise for each X-ray detection element DU in the main pixel area A1 from the transferred two-dimensional temperature distribution data. The temperature fluctuation noise of each X-ray detection element DU is transferred to the temperature fluctuation noise removing unit 30.
　温度変動ノイズ除去部３０では、画像メモリ部２３に保管されている温度非変動ノイズ成分γを除去した主画素電圧信号から、対応する温度変動ノイズ算出部２９から転送される温度変動ノイズを除去することで、Ｘ線検出素子ＤＵごとのＸ線透過画像信号を得ることができる。Ｘ線透過画像信号は画像構成部２６へ転送される。 The temperature fluctuation noise removal unit 30 removes the temperature fluctuation noise transferred from the corresponding temperature fluctuation noise calculation unit 29 from the main pixel voltage signal from which the temperature non-fluctuation noise component γ stored in the image memory unit 23 is removed. Thus, an X-ray transmission image signal for each X-ray detection element DU can be obtained. The X-ray transmission image signal is transferred to the image construction unit 26.
　画像構成部２６では、転送されたＸ線透過画像信号より、被検体ＭのＸ線透視画像を構成する。構成されたＸ線透視画像は、主制御部６を介して表示部９に表示される。 The image construction unit 26 constructs an X-ray fluoroscopic image of the subject M from the transferred X-ray transmission image signal. The configured X-ray fluoroscopic image is displayed on the display unit 9 via the main control unit 6.
　以上のようにして得られたＸ線透視画像は、温度変動ノイズおよび温度非変動ノイズのどちらも除去されているので、鮮明な画像を得ることができる。また、撮像環境の温度に変動されないＸ線透視画像を得ることができる。また、動画を撮像時でも、リアルタイムで温度変動ノイズを除去することができる。また、変換層１７の温度を２次元温度分布として測定できる。 Since the X-ray fluoroscopic image obtained as described above has both temperature fluctuation noise and temperature non-variation noise removed, a clear image can be obtained. Further, it is possible to obtain an X-ray fluoroscopic image that is not changed by the temperature of the imaging environment. In addition, even when capturing a moving image, temperature fluctuation noise can be removed in real time. Further, the temperature of the conversion layer 17 can be measured as a two-dimensional temperature distribution.
　この発明は、上記実施形態に限られることはなく、下記のように変形実施することができる。 The present invention is not limited to the above embodiment, and can be modified as follows.
　（１）上述した実施例では、各Ｘ線検出画素ＤＵの温度変動ノイズを算出していたが、図７に示すように、複数個のＸ線検出画素ＤＵで構成される領域ごとの温度変動ノイズを算出してもよい。つまり、同一の検出画素領域内の各Ｘ線検出画素ＤＵの温度変動ノイズを同一の値とする。図７ではＦＰＤ３３のＸ線検出部ＸＤ２の主画素領域がＡ２～Ａ１０の９つの検出画素領域に分割されている。主画素領域をいくつの検出画素領域に分割するかは、２次元温度分布の正確さを求めるか、２次元温度分布の測定時間の短縮を求めるかによって任意に決めればよい。これより、検出画素領域単位で、Ｘ線変換層１７に流れる暗電流の平均値と温度との関係式またはルックアップテーブルを作成しておけばよい。さらに、Ｘ線検出素子ＤＵごとに測定された温度から温度変動ノイズを算出するよりも、検出画素領域ごとに温度変動ノイズを算出するので処理時間の短縮をすることができる。 (1) In the embodiment described above, the temperature fluctuation noise of each X-ray detection pixel DU is calculated. However, as shown in FIG. 7, the temperature fluctuation for each region constituted by a plurality of X-ray detection pixels DU. Noise may be calculated. That is, the temperature fluctuation noise of each X-ray detection pixel DU in the same detection pixel region is set to the same value. In FIG. 7, the main pixel area of the X-ray detector XD2 of the FPD 33 is divided into nine detection pixel areas A2 to A10. The number of detection pixel regions into which the main pixel region is divided may be arbitrarily determined depending on whether the accuracy of the two-dimensional temperature distribution is obtained or the measurement time of the two-dimensional temperature distribution is reduced. Accordingly, a relational expression or a look-up table between the average value of the dark current flowing through the X-ray conversion layer 17 and the temperature may be created for each detection pixel region. Further, since the temperature fluctuation noise is calculated for each detection pixel region, the processing time can be shortened, rather than calculating the temperature fluctuation noise from the temperature measured for each X-ray detection element DU.
　（２）上述した実施例では、補正用画素領域Ｂ１はＸ線検出部ＸＤ１、２の左片端に配置しているが、上下左右のどの片端に配置してもよい。また、片端だけに限らず、図８に示すようにＦＰＤ３４のＸ線検出部ＸＤ３の左右両端に補正用画素領域Ｂ１およびＢ２があってもよい。この場合、左右両端だけに限らず上下両端でもよい。このように、Ｘ線検出部ＸＤ３の両端に補正用画素領域を設けた場合、両端の補正用画素領域Ｂ１およびＢ２の補正用電圧信号の平均値を用いてもよいし、主画像領域も２つに分割して主画像領域Ａ１１およびＡ１２とそれぞれ独立してノイズ補正をかけてもよい。また、図９に示すようにＦＰＤ３５のＸ線検出部ＸＤ４の上下左右全ての端部に補正用画素領域Ｂ３～Ｂ６を配置してもよい。つまり、Ｘ線検出部ＸＤ４の四辺に沿って端部に補正用画素領域Ｂ３～Ｂ６を配置する。これより、主画素領域Ａ１３における２次元温度分布の算出精度を向上させることができる。 (2) In the above-described embodiment, the correction pixel area B1 is arranged at the left end of the X-ray detection units XD1 and XD2, but it may be arranged at any one of the upper, lower, left and right ends. Further, not only one end but also correction pixel regions B1 and B2 may be provided at both left and right ends of the X-ray detection unit XD3 of the FPD 34 as shown in FIG. In this case, the upper and lower ends are not limited to the left and right ends. As described above, when the correction pixel regions are provided at both ends of the X-ray detection unit XD3, the average value of the correction voltage signals of the correction pixel regions B1 and B2 at both ends may be used, and the main image region is also 2 It may be divided into two and noise correction may be applied independently of the main image areas A11 and A12. Further, as shown in FIG. 9, correction pixel regions B3 to B6 may be arranged at all the upper, lower, left and right ends of the X-ray detection unit XD4 of the FPD 35. That is, correction pixel regions B3 to B6 are arranged at the end portions along the four sides of the X-ray detection unit XD4. Thereby, the calculation accuracy of the two-dimensional temperature distribution in the main pixel region A13 can be improved.
　（３）上述した実施例では、補正用画素領域Ｂ１からの補正用電圧信号を基に変換層温度算出部２７においてＸ線変換層１７の温度を測定していたが、Ｘ線照射前に全てのＸ線検出素子ＤＵの暗画像電圧信号を基に、変換層温度算出部２７にて各Ｘ線検出素子ＤＵ内のＸ線変換層１７の温度を測定してもよい。 (3) In the above-described embodiment, the temperature of the X-ray conversion layer 17 is measured by the conversion layer temperature calculation unit 27 based on the correction voltage signal from the correction pixel region B1. The temperature of the X-ray conversion layer 17 in each X-ray detection element DU may be measured by the conversion layer temperature calculation unit 27 based on the dark image voltage signal of the X-ray detection element DU.
　（４）上述した実施例では、補正用画素領域Ｂ１からの補正用電圧信号を基にＸ線変換層１７の温度を測定していたが、補正用画素領域Ｂ１に温度センサを直接取り付けて、温度センサからの温度データを基に、主画素領域Ａ１の温度変動ノイズを除去してもよい。 (4) In the above-described embodiment, the temperature of the X-ray conversion layer 17 is measured based on the correction voltage signal from the correction pixel region B1, but a temperature sensor is directly attached to the correction pixel region B1, Based on the temperature data from the temperature sensor, the temperature fluctuation noise in the main pixel region A1 may be removed.
　（５）上述した実施例では、Ｘ線検出素子ＤＵはＸ線に感応するＸ線感応型半導体であったが、光感応型半導体を採用すれば、同じ構成にて変換層の温度を測定することができる光撮像装置を製作することができる。 (5) In the embodiment described above, the X-ray detection element DU is an X-ray sensitive semiconductor that is sensitive to X-rays. However, if a light-sensitive semiconductor is employed, the temperature of the conversion layer is measured with the same configuration. An optical imaging device that can be used can be manufactured.

Claims (11)

  1. 　光または放射線撮像装置において、
    　光または放射線を電荷信号へ変換する変換層と、
    　前記変換層を２次元マトリックス状に分割した検出素子ごとに前記電荷信号を読み出す読み出し手段と、
    　前記読み出し手段から読み出される電荷信号を電圧信号に変換する電荷電圧変換手段と、
    　前記電圧信号に含まれる前記変換層を流れる暗電流成分を基に、前記変換層の温度を求める変換層温度算出部と
    　を備えたことを特徴とする光または放射線撮像装置。     In a light or radiation imaging device,
    A conversion layer that converts light or radiation into a charge signal;
    Read means for reading out the charge signal for each detection element obtained by dividing the conversion layer into a two-dimensional matrix;
    Charge voltage conversion means for converting a charge signal read from the reading means into a voltage signal;
    A light or radiation imaging apparatus comprising: a conversion layer temperature calculation unit that obtains a temperature of the conversion layer based on a dark current component flowing through the conversion layer included in the voltage signal.
  2. 　請求項１に記載の光または放射線撮像装置において、
    　前記変換層温度算出部は、前記電圧信号に含まれる前記変換層を流れる暗電流成分と温度との関係式により、前記変換層の温度を求める
    　ことを特徴とする光または放射線撮像装置。     The light or radiation imaging apparatus according to claim 1.
    The conversion layer temperature calculation unit obtains the temperature of the conversion layer from a relational expression between a dark current component flowing through the conversion layer and the temperature included in the voltage signal.
  3. 　請求項１に記載の光または放射線撮像装置において、
    　前記変換層温度算出部は、前記電圧信号に含まれる前記変換層の暗電流成分と温度との対応表により、前記変換層の温度を求める
    　ことを特徴とする光または放射線撮像装置。     The light or radiation imaging apparatus according to claim 1.
    The conversion layer temperature calculation unit obtains the temperature of the conversion layer from a correspondence table between the dark current component of the conversion layer and the temperature included in the voltage signal.
  4. 　請求項１から３のいずれか１つに記載の光または放射線撮像装置において、
    　前記変換層は主画素領域と補正用画素領域に分けられ、
    　前記変換層温度算出部により求められた前記補正用画素領域内の前記変換層の温度から、前記主画素領域内の前記変換層における２次元温度分布を算出する温度分布算出部
    　を備えたことを特徴とする光または放射線撮像装置。     The light or radiation imaging apparatus according to any one of claims 1 to 3,
    The conversion layer is divided into a main pixel region and a correction pixel region,
    A temperature distribution calculation unit that calculates a two-dimensional temperature distribution in the conversion layer in the main pixel region from the temperature of the conversion layer in the correction pixel region obtained by the conversion layer temperature calculation unit; Feature light or radiation imaging device.
  5. 　請求項１から３のいずれか１つに記載の光または放射線撮像装置において、
    　前記変換層は主画素領域と補正用画素領域に分けられ、
    　さらに前記主画素領域は複数の検出画素領域に分けられ、
    　前記変換層温度算出部により求められた前記補正用画素領域内の前記変換層の温度から、前記検出画素領域ごとの前記変換層における２次元温度分布を算出する温度分布算出部を備えたことを特徴とする光または放射線撮像装置。     The light or radiation imaging apparatus according to any one of claims 1 to 3,
    The conversion layer is divided into a main pixel region and a correction pixel region,
    Further, the main pixel region is divided into a plurality of detection pixel regions,
    A temperature distribution calculation unit that calculates a two-dimensional temperature distribution in the conversion layer for each detection pixel region from the temperature of the conversion layer in the correction pixel region obtained by the conversion layer temperature calculation unit; Feature light or radiation imaging device.
  6. 　請求項４または５に記載の光または放射線撮像装置において、
    　前記変換層における２次元温度分布から、前記検出素子それぞれの暗電流成分を求める暗電流成分算出部と、
    　前記検出素子ごとに送られる前記電圧信号からアンプノイズを除去するアンプノイズ除去部と、
    　前記アンプノイズが除去された前記電圧信号から、前記検出素子それぞれの暗電流成分を除去する暗電流成分除去部と
    　を備えたことを特徴とする光または放射線撮像装置。     The light or radiation imaging apparatus according to claim 4 or 5,
    A dark current component calculation unit for obtaining a dark current component of each of the detection elements from a two-dimensional temperature distribution in the conversion layer;
    An amplifier noise removing unit that removes amplifier noise from the voltage signal sent for each detection element;
    A light or radiation imaging apparatus comprising: a dark current component removing unit that removes a dark current component of each of the detection elements from the voltage signal from which the amplifier noise has been removed.
  7. 　請求項４から６のいずれか１つに記載の光または放射線撮像装置において、
    　前記補正用画素領域が前記変換層の片端に配置されている
    　ことを特徴とする光または放射線撮像装置。     The light or radiation imaging apparatus according to any one of claims 4 to 6,
    The correction pixel region is arranged at one end of the conversion layer. A light or radiation imaging apparatus, wherein:
  8. 　請求項４から６のいずれか１つに記載の光または放射線撮像装置において、
    　前記補正用画素領域が前記変換層の両端に配置されている
    　ことを特徴とする光または放射線撮像装置。     The light or radiation imaging apparatus according to any one of claims 4 to 6,
    The light or radiation imaging apparatus, wherein the correction pixel region is disposed at both ends of the conversion layer.
  9. 　請求項４から６のいずれか１つに記載の光または放射線撮像装置において、
    　前記補正用画素領域が前記変換層の四辺に沿って端部に配置されている
    　ことを特徴とする光または放射線撮像装置。     The light or radiation imaging apparatus according to any one of claims 4 to 6,
    The light or radiation imaging apparatus, wherein the correction pixel region is disposed at an end portion along four sides of the conversion layer.
  10. 　請求項１から９のいずれか１つに記載の光または放射線撮像装置において、
    　前記光または放射線変換層は、ＣｄＴｅまたはＣｄＺｎＴｅを主原料とする化合物半導体である
    　ことを特徴とする光または放射線撮像装置。     In the light or radiation imaging device according to any one of claims 1 to 9,
    The light or radiation imaging device, wherein the light or radiation conversion layer is a compound semiconductor using CdTe or CdZnTe as a main material.
  11. 　請求項１から９のいずれか１つに記載の光または放射線撮像装置において、
    　前記変換層は、アモルファスセレンである
    　ことを特徴とする光または放射線撮像装置。     In the light or radiation imaging device according to any one of claims 1 to 9,
    The conversion layer is amorphous selenium. A light or radiation imaging apparatus, wherein:
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